The present invention relates to a method for sealingly connecting a smaller diameter sewer pipe to a larger pipe or manhole through the use of an elastomeric gasket, and in particular to the method for inserting the gasket into the opening prior to connection of the pipe.
In order to provide watertight connections between sewer pipes and manholes, it has become common practice to employ elastomeric rubber gaskets which are compressively clamped to the pipe and to the inner surface of the manhole opening. Since the gaskets are flexible, they tolerate a considerable amount of misalignment between the pipe and opening occurring during installation or at some later time due to soil settling around the manhole or pipe.
One such gasket is disclosed in U.S. Pat. No. 3,787,078 and comprises an elastomeric ring having resilient flexible flanges which provide a fluid-tight seal when pressed into a tapered opening in the manhole. The sewer pipe, which is equipped with such a ring or gasket, is crowded into the tapered passage so that the flanges deflect to engage the walls of the passage and provide a seal.
Another prior art gasket is disclosed in U.S. Pat. No. 3,958,313 and comprises a flexible boot having an external contracting clamp on one end for clamping the gasket to a sewer pipe or the like, and an internal expanding clamp on the opposite end. To connect the boot to the manhole opening, the boot is located within the opening with the internal clamp in its non-expanded state, and an over-center toggle mechanism is then locked to expand the clamp so as to compress the boot between it and the internal surface of the opening. One disadvantage to this last device is that there is always the possibility of failure of the toggle mechanism resulting from corrosion or chemical attack caused by the effluent carried by the pipe or by environmental conditions. Furthermore, shifting of the pipe or manhole during installation or subsequently through shifting of the supporting ground may cause unlocking of the toggle mechanism. Obviously, this would result in loss of the seal between the gasket and opening thereby causing leakage.
In the method disclosed in the aforementioned application Ser. No. 915,770, there is provided an elastomeric annular gasket which has an outer diameter slightly larger than the inner diameter of the manhole opening and includes a one-piece ring received therein. The gasket and ring assembly is pressed into the opening by means of a jack so as to compress the gasket between the opening and the annular ring thereby establishing a watertight seal between the gasket and opening. The sewer pipe is then connected to the other end of the gasket by means of a standard compressive clamp.
The jacking mechanism utilized to press the gasket and ring assembly into the opening is of the extensible type. The jacking mechanism is braced against the wall of the manhole directly opposite the opening, and is then extended so as to press the gasket and ring assembly into the opening. Difficulty arises when the manhole is of a size or shape which does not easily accommodate the jack, or where the person who must operate the jack cannot easily fit into the manhole. This would be the case where one sewer pipe is connected to another sewer pipe which, although of a larger diameter, is still not sufficiently large to accommodate the entry of a workman for the purpose of operating the extensible jack.